> For the complete documentation index, see [llms.txt](https://liuxue2010.gitbook.io/data-structure-and-algorithms/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://liuxue2010.gitbook.io/data-structure-and-algorithms/binary-tree-and-divide-conquer/binary-tree-level-order-traversal-ii.md).

# Binary Tree Level Order Traversal II

Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to right, level by level from leaf to root).

## Example

Given binary tree {3,9,20,#,#,15,7},

```
    3
   / \
  9  20
    /  \
   15   7
```

return its bottom-up level order traversal as:

```
[
  [15,7],
  [9,20],
  [3]
]
```

## Solution

```
class Solution:
    """
    @param root: The root of binary tree.
    @return: buttom-up level order in a list of lists of integers
    """
    def levelOrderBottom(self, root):
        # write your code here
        self.results = []
        if not root:
            return self.results
        q = [root]
        while q:
            new_q = []
            self.results.append([n.val for n in q])
            for node in q:
                if node.left:
                    new_q.append(node.left)
                if node.right:
                    new_q.append(node.right)
            q = new_q
        return list(reversed(self.results))
```